标题： 矮不规则星系IC10的径向范围 显示英文标题

标题： On the radial extent of the dwarf irregular galaxy IC10

摘要： 我们提供了新的深度且精确的空间（哈勃空间望远镜上的高级巡天相机——宽视场行星相机2）和地面观测（昴星团望远镜上的Suprime-Cam，加拿大-法国-夏威夷望远镜上的Mega-Cam）光度和天体测量数据，用于本地集团矮不规则星系IC10。我们确认了当从中心向最外侧区域移动时，年轻恒星种群显著减少。我们发现IC10的潮汐半径明显大于之前估计的$r_t \lesssim$10\min 。通过使用基于Suprime-Cam数据的$I$,\vmi 色-星等图，我们在距离星系中心18-23$'$的径向距离内检测到了大量红巨星（RG）恒星。在红巨星分支顶端处观测到的恒星计数（Mega-Cam数据）与银河系模型预测的恒星计数之间的比率表明，在距离中心34-42\min 处至少在3$\sigma$水平上存在恒星计数过剩。 这一发现支持了这样的假设，即覆盖银河系超过一度的巨大的H{\size{I}}云与IC10 \citep{huchtmeier79,cohen79}相关。 我们还提供了总光度（$L_V\sim9\times$$10^7$ $L_\odot$ ，$M_V$$\sim$ -15.1 mag）的新估计，这与文献中类似的估计一致。 如果我们限制在有旋转速度测量的区域（r$\approx13'$），我们会发现质量与光度比 ($\sim$10 $M_\odot$ $L_\odot$ ) 比以前的估计至少大一个数量级。 新的估计应谨慎对待，因为它仅基于星系身体的一小部分。 显示英文摘要

摘要： We present new deep and accurate space (Advanced Camera for Surveys -- Wide Field Planetary Camera 2 at the Hubble Space Telescope) and ground-based (Suprime-Cam at Subaru Telescope, Mega-Cam at Canada-France-Hawaii Telescope) photometric and astrometric data for the Local Group dwarf irregular IC10. We confirm the significant decrease of the young stellar population when moving from the center toward the outermost regions. We find that the tidal radius of IC10 is significantly larger than previous estimates of $r_t \lesssim$ 10\min. By using the $I$,\vmi\ Color Magnitude Diagram based on the Suprime-Cam data we detect sizable samples of red giant (RG) stars up to radial distances of 18-23$'$ from the galactic center. The ratio between observed star counts (Mega-Cam data) across the tip of the RG branch and star counts predicted by Galactic models indicate a star count excess at least at a 3$\sigma$ level up to 34-42\min\ from the center. This finding supports the hypothesis that the huge H{\size{I}} cloud covering more than one degree across the galaxy is associated with IC10 \citep{huchtmeier79,cohen79}. We also provide new estimates of the total luminosity ($L_V\sim9\times$$10^7$ $L_\odot$, $M_V$$\sim$-15.1 mag) that agrees with similar estimates available in the literature. If we restrict to the regions where rotational velocity measurements are available (r$\approx13'$), we find a mass-to-light ratio ($\sim$10 $M_\odot$ $L_\odot$) that is at least one order of magnitude larger than previous estimates. The new estimate should be cautiously treated, since it is based on a minimal fraction of the body of the galaxy.